Can't speak for your Audi but the espace was dead easy (even though I just watched someone else do it for me - but it was a free service!) After using it the first time check the bolts are still done up tight, and mybe the second/third time too.
I would spend the extra money and go for a witter tow bar, I fitted one to my transit van and it was simple, the electrics was the hardest thing to do but that was easy just took a bit of time finding the correct wires to connect to.
Also some of the cheaper makes of tow bars suggest that you only tow a certain weight/type of trailer.
Some are easy to fit, some are hard. I fitted one to my Fiat, took me most of a sunday afternoon and some seriously large drill bits. Some cars have the holes already there and you literally just bolt the thing on. My Fiat didn't!!